1. Field of the Invention
The invention relates to hydropneumatic apparatus as used for pump pulsation damping, pipeline shock absorption, pipeline fluid thermal expansion compensation, and the like. While referred to as a hydropneumatic pulse interceptor such an apparatus is also referred to as a hydropneumatic accumulator.
2. Description of the Prior Art
It is desirable to prevent cavitation from occurring within positive displacement pumping chambers. Cavitation occurs on the suction stroke of positive displacement pumps because of the need to generate energy to accelerate the flow of liquid into the pumping chamber. The energy necessary to accelerate this flow may be considerable in the situation involving a long length of suction line and consequently a substantial volume of liquid. The ambient pressure applied to the liquid may not be sufficient to cause the acceleration of the suction flow. In these circumstances, the suction stroke of the pump causes the vapor of the liquid to come out of solution and hence for at least a portion of the suction stroke, the pumping chamber is not being filled. As a result of these circumstances, part of the pump delivery stroke is merely dissipated and results in forcing the vapor back into solution. The pump plunger then effectively encounters a solid wall of liquid which causes an abrupt shock or pulse to be emitted from the discharge port of the pump.
It is known that when the circumstances mentioned above are prevented, the horsepower required to drive the pump can be reduced and the pump discharge flow can be sinusoidal rather than square wave in character. Various types of hydropneumatic accumulators are known in the prior art. Applicant's prior U.S. Pat. No. 3,537,357, for example, teaches a hydropneumatic accumulator having a cylinder divided by a sliding piston which mounts a flexible diaphragm which separates the compressible fluid from the incompressible fluid in the cylinder. The entry and exhaust ports are located at one end of the cylinder and on either side of the longitudinal center line of the accumulator. The compressible fluid gains contact with the diaphragm by passing through the center of a conical end portion of the piston. While the hydropneumatic accumulator described in patent 3,537,357 has found useful application in the industry, it has been noted that the conical end of the piston tends to deflect the pulses to some extent and this action prevents maximum cooperation of the incompressible fluid with the diaphragm. Furthermore, the arrangement described in U.S. Pat. No. 3,537,357 is not suitable for use with liquids containing solid particles. Nevertheless, the arrangement described in U.S. Pat. No. 3,537,357 does prevent the mentioned diaphragm from extruding into the outlet port which is a desirable characteristic for any accumulator utilizing a diaphragm.
U.S. Pat. No. 3,483,893 teaches another type of hydropneumatic accumulator having a single port which operates as both an inlet port and an outlet port for admitting and discharging the incompressible fluid being operated on by the accumulator. This single port within the accumulator connects through multiple passages to the interior of a flexible bag which is adapted to receive the incompressible fluid and is surrounded by a chamber filled with compressible fluid. The construction associated with U.S. Pat. No. 3,483,893 introduces substantial costs because of having to make multiple entries for admitting the incompressible fluid to the bag and because of requiring an anti-extrusion valve plate for each of the seats associated with the several passages that admit and discharge the incompressible fluid to and from the bag so as to prevent any portion of the bag being extruded through any of such multiple entries and passages. Also, the construction described in U.S. Pat. No. 3,483,893 involves providing a bag of relatively complex cross section in order to effect an arcuate swinging of the mentioned anti-extrusion valve plates toward and away from the seats associated with the multiple entries and passages.
U.S. Pat. No. 4,166,478 teaches both single port and twin port-type hydropneumatic accumulators. The accumulator construction employed in U.S. Pat. No. 4,166,478, like the construction as employed in U.S. Pat. 3,483,893, employs a bladder into which the incompressible fluid is admitted and from which such incompressible fluid is discharged as the line pressure conditions change. A perforated rigid shell member projects upwardly into the bottom of the bladder to prevent extrusion of the bladder into the port when the incompressible liquid is being discharged.
Another type of hydropneumatic accumulator has been sold by the assignee of the present application FLOWCHEM, Inc., 1000 Instrument Drive, Rocky Mount, N.C. 27801 under the trademark Hydroflex. One version of the Hydroflex accumulator comprises a cylinder one end of which is closed by a closely fitting plug which also supports a bag within the cylinder. The opposite end of the cylinder is fitted with a single port through which the incompressible fluid is admitted and discharged into a chamber surrounding the bag with the bag being filled with a compressible fluid. The accumulator bag mounts at its closed end opposite the single port a so-called button valve having a circular plate member of larger diameter than the port and which acts to prevent extrusion of the bag into the port when the incompressible fluid is being discharged through the port from the cylinder. This version of the Hydroflex accumulator however does not provide either flow through the accumulator nor does it allow flow into the accumulator when the button valve is sealing the mentioned single port.
Within the last few weeks, prior to this application, there has appeared another type of hydropneumatic accumulator sold by FLOWCHEM, Inc., and sold under the trademark Jumboflex. The Jumboflex accumulator, like the Hydroflex accumulator described above, has a cylinder with one end closed by a close fitting plug that supports a bag containing a compressible fluid. The opposite end of the cylinder is provided with a single port for admitting and discharging the incompressible fluid being operated on by the accumulator. The Jumboflex accumulator also incorporates an antiextrusion button valve which operates in the manner described for the Hydroflex accumulator. Increased tension on the bag when in its most extended position is provided by a suspension strap mounted within the bag and extending between the mentioned cylinder closure plug and a fitting within the bag and forming part of the button valve. The use of this suspension strap assists in preventing the button valve from prematurely covering the single port before the incompressible fluid has been discharged.
With the foregoing in mind, the object of the hydropneumatic accumulator of the invention has the severalfold purpose of providing an accumulator having extreme pressure sensitivity, providing an accumulator having a flow-through path enabling the extreme pressure sensitivity of the accumulator to act upon the flow, to provide an accumulator which does not intercept and shut off the flow when in a non-operational mode, to provide an accumulator having both inlet and outlet ports communicating with a portion of the cylinder adapted to receive and discharge the incompressible fluid and arranged so that the outlet port can be completely sealed without closing the inlet port, to provide an accumulator that can be manufactured from readily available materials compatible with the range of different liquids normally encountered in the application of accumulators and to provide an accumulator in which the bag or membrane member employed to contain the compressible fluid is adapted to be moldable from readily available elastomers and in a form of relatively simple cross section.